A. The best counters to use to check the performance of your disks are the average latency for reads and writes on the logical disks used to store the VMS on the actual Hyper-V host, and the same counters within the guest OSs. Anything above 15ms would be considered sub-optimal and counters staying above this time for long would indicate disk performance problems. On my Hyper-V host, I can see a few instances (but not many, and only for split seconds), indicating that disk performance isn't a problem on the system. Looking at the same counters within VMs also showed no problems.
Launch Performance Monitor (perfmon.exe) and, under Logical Disk, select Avg. Disk sec/Read and Avg. Disk sec/Write, then select the volumes to monitor.